An Upper East Side medical assistant is suing her obstetrician boss, claiming she was fired for missing work — because she was in labor.

Jennifer E. Mercado, of the Bronx, started working for Dr. Gabriela Ana Olaru at her E. 75th Street offices in March 2011.

Mercado discovered she was pregnant a month later and informed her Romanian-educated boss, whose first response was to ask if “she wanted to keep the baby,” the Manhattan Supreme Court suit alleges.

When Mercado said she did the doctor allegedly demanded to know her “plans for birth control after she delivered.”

The $13-an-hour assistant — who gave injections to patients, measured their height and weight and collected medical samples — was not provided health insurance by her employer so she had to seek prenatal treatments at a Bronx clinic that accepted Medicaid and was only open on weekdays, according to the court papers.

Mercado said that she would bring a doctor’s note to explain her tardiness and work late to make up the time she missed.

Still, “Dr. Olaru began to harass her and express frustration and annoyance at Ms. Mercado’s late arrival to work after the appointments,” the suit claims.

The OB-GYN’s attitude turned Mercado into an emotional wreck, she says in the suit, adding that she even skipped check ups, fearing she would lose her job.

“As a result of her professional expertise Dr. Olaru knew that it was important for Ms. Mercado to attend her prenatal appointments.”

Then in September Mercado started having painful contractions and called the office from the Bronx hospital where she was in labor.

The office assistant allegedly told her she was fired because Dr. Olaru said she “can’t take it anymore.”

Mercado said a second employee was ousted after returning from maternity leave that summer and Olaru replaced both of them with staffers who didn’t have young children or who weren’t pregnant.